In oil well drilling operations, a drill bit can be mounted on the end of an elongated rotating drill string which turns the bit and causes it to cut away the underlying earth and rock formations. During this operation, a drilling mud is continuously pumped down through the drill string and into the region around the drill bit and then back up to the surface. This drilling mud is typically made up of clays, chemical additives and/or an oil or water base and performs two important functions. First, the drilling mud acts as a coolant and lubricates the drill bit during operation and it collects the drill cuttings and carries them back to the surface of the well. Second, the drilling mud also serves to maintain a hydrostatic pressure, which prevents pressurized gases from the earth from blowing out through the drilled well. In addition, the mud may pick up and entrain gases present in the bottom of the well and deliver them to the surface along with the drill cuttings.
Drilling mud generally constitutes a liquid carrier, typically water or diesel oil, which is mixed with additives. In the case of a water-based mud, this may include bentonite clay and various chemicals. The mud carries out several functions for assisting in the drilling process, including carrying away cuttings and fine solids produced by the drill bit as it bores through the rock. Entrained solids raise the mud's density and viscosity, leading to many drilling problems, including a reduced rate of penetration, loss of mud downhole and filter cake buildup. The portion of the drilling mud being returned from the well which includes various gaseous components to be analyzed must be separated from the mud.
It has been common in the past to provide a log of the drilling operation that will permit the nature of the earth formation through which the drill bit is penetrating. The log enables the drilling operator to ascertain the presence of oil or gas in the formation being drilled and also the location of such oil or gas in the well. As part of this logging operation, samples of the drill cuttings from predetermined depths of the well are collected and analyzed. Generally, these samples can be collected to represent a desired interval of drilling, such as every ten feet of well drilled or every thirty feet drilled.
In a majority of prior art mud logging systems, the information recorded from the drilling mud reaching the surface of the well, is generally done on a manual basis. All of the measurements and the measuring equipment require constant supervision so a logging operation generally involves two mud loggers each working alternate twelve-hour shifts. The well mud logging techniques have also made use of gas chromatography to ascertain the presence of different hydrocarbon species in the mud being returned. The gas chromatography technique involves taking samples of gas from the drilling mud and passing that gas through special columns filled with materials that allow different gases to flow at different rates. A further disadvantage of the prior art chromatographic gas analysis technique results from the fact that it is not possible to separate all of the hydrocarbon gas from the returning mud and therefore it is not possible with chromatographic analysis to ascertain the actual concentration of any species in the mud.
Based on the foregoing it is believed that a need exists for an improved system and method for analyzing the concentrations and amounts of one or more different gases from the mud produced by drilling an oil well.